Burley tobacco products having reduced nitrosamine content

ABSTRACT

A method of treating tobacco to reduce the content of, or prevent formation of, harmful nitrosamines which are normally found in tobacco is disclosed. The method includes the step of subjecting at least a portion of the plant, while the portion is uncured and in a state susceptible to having the amount of nitrosamines reduced or formation of nitrosamines arrested, to a controlled environment capable of providing a reduction in the amount of nitrosamines or prevention of the formation of nitrosamines, for a time sufficient to reduce the amount of or substantially prevent the formation of at least one nitrosamine, wherein the controlled environment is provided by controlling at least one of humidity, rate of temperature change, temperature, airflow, CO level, CO 2  level, O 2  level, and arrangement of the tobacco plant. Tobacco products and an apparatus for producing such tobacco products are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/141,117,filed May 9, 2002, which is a continuation of application Ser. No.09/668,144, filed Sep. 25, 2000, now U.S. Pat. No. 6,425,401, which is acontinuation of application Ser. No. 09/397,018, filed Sep. 15, 1999,now U.S. Pat. No. 6,202,649, which is based on provisional applicationSer. No. 60/100,372, filed Sep. 15, 1998, and which is acontinuation-in-part of application Ser. No. 08/998,043, filed Dec. 23,1997, now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 08/879,905, filed Jun. 20, 1997, now U.S. Pat. No.6,135,121, which in turn is a continuation-in-part of Ser. No.08/757,104, filed Dec. 2, 1996, now U.S. Pat. No. 5,803,081. U.S.provisional application Ser. No. 60/100,372, U.S. application Ser. Nos.08/998,043 and 08/879,905, and U.S. Pat. No. 5,803,081 are allincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an improved method of treating tobaccoto reduce the content of, or to prevent the formation of, harmfulnitrosamines, which are normally found in tobacco. The present inventionalso relates to tobacco products having low nitrosamine content.

BACKGROUND OF THE INVENTION

Prior attempts to reduce tar and harmful carcinogenic nitrosaminesprimarily have included the use of filters in smoking tobacco. Inaddition, attempts have been made to use additives to block the effectsof harmful carcinogens in tobacco. These efforts have failed to reducethe oncologic morbidity associated with tobacco use. It is known thatfresh-cut, green tobacco has virtually no nitrosamine carcinogens. See,e.g., Wiernik et al, “Effect of Air-Curing on the Chemical Compositionof Tobacco,” Recent Advances in Tobacco Science, Vol. 21, pp. 39 etseq., Symposium Proceedings 49th Meeting Tobacco Chemists' ResearchConference, Sep. 24-27, 1995, Lexington, Ky. (hereinafter “Wiernik etal.”). On the other hand, cured tobacco products obtained according toconventional methods are known to contain a number of nitrosamines,including the harmful carcinogens N′-nitrosonornicotine (NNN) and4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK). It is widelyaccepted that such nitrosamines are formed post-harvest, during theconventional curing process, as described further herein. Unfortunately,fresh-cut green tobacco is unsuitable for smoking or other consumption.

It is believed that tobacco-specific nitrosamines (TSNAs) are formedprimarily during the curing process. While not wishing to be bound bytheory, it is believed that the amount of tobacco-specific nitrosamine(TSNA) in cured tobacco leaf is dependent on the accumulation ofnitrites, which accumulate during the death of the plant cell and areformed during curing by the reduction of nitrates under conditionsapproaching an anaerobic (oxygen deficient) environment. It is believedthat the reduction of nitrates to nitrites occur by the action of themicro flora on the surface of the leaf under anaerobic conditions, andit is also believed that this reduction is particularly pronounced undercertain conditions (e.g., humid conditions). Furthermore, during thecuring process, the tobacco leaf emits carbon dioxide, which can furtherdilute oxygen levels in the environment.

Once the nitrites are formed, these compounds are believed to combinewith various tobacco alkaloids, including pyridine-containing compounds,to form carcinogenic nitrosamines.

In 1993 and 1994, Burton et al. at the University of Kentucky carriedout certain experiments regarding TSNA, as reported in the Abstract,“Reduction of Nitrite-Nitrogen and Tobacco N′-Specific Nitrosamines InAir-Cured Tobacco By Elevating Drying Temperatures,” Agronomy &Phytopathology Joint Meeting, CORESTA, Oxford 1995. Burton et alreported that drying harvested tobacco leaves for 24 hours at 71° C., atvarious stages of air curing, including end of yellowing (EOY), EOY+3,EOY+5, etc. resulted in some reduction of nitrosamine levels. Referenceis also made to freeze drying and microwaving of certain samples,without detail or results. It has been confirmed that in the actual workunderlying this Abstract, carried out by Burton et al. at the Universityof Kentucky, the microwave work was considered unsuccessful. Certainaspects of Burton et al.'s 1993-94 study are reported in Wiernik et al,supra, at pages 54-57, under the heading “Modified Air-Curing.” TheWiernik et al article postulates that subjecting tobacco leaf samples,taken at various stages of air-curing, to quick-drying at 70° C. for 24hours, would remove excess water and reduce the growth ofmicroorganisms; hence, nitrite and tobacco-specific nitrosamine (TSNA)accumulation would be avoided. In Table II at page 56, Wiernik et al.includes some of Burton et al's summary data on lamina and midribnitrite and TSNA contents in the KY160 and KY171 samples. Data from thefreeze-drying and the quick-drying tests are included. The articlecontains the following conclusion:

-   -   It can be concluded from this study that it may be possible to        reduce nitrite levels and accumulation of TSNA in lamina and        midrib by applying heat (70° C.) to dark tobacco after loss of        cell integrity in the leaf. Drying the tobacco leaf quickly at        this stage of curing reduces the microbial activity that occurs        during slow curing at ambient temperature. It must be added,        however, that such a treatment lowers the quality of the tobacco        leaf.

Id. at page 56. The Wiernik et al. article also discusses traditionalcuring of Skroniowski tobacco in Poland as an example of a 2-step curingprocedure. The article states that the tobacco is first air-cured and,when the lamina is yellow or brownish, the tobacco is heated to 65° C.for two days in order to cure the stem. An analysis of tobacco producedin this manner showed that both the tobacco-specific nitrosamine (TSNA)and the nitrite contents were low, i.e., in the range of 0.6-2.1micrograms per gram and less than 10 micrograms per gram, respectively.Wiernik et al. theorized that these results were explainable due to therapid heating which does not allow further bacterial growth. Wiernik etal. also noted that tobacco-specific nitrosamine (TSNA) and nitritecontents of 0.2 microgram per gram and less than 15 micrograms per gram,respectively, were obtained for tobacco subjected to air-curing inPoland.

In practice, tobacco leaves are generally cured according to one ofthree methods. First, in some countries, such as China, a variation ofthe flue curing process (described below) is still being used on acommercial scale to cure tobacco leaves. Specifically, this variation ofthe flue curing process features the use of a heat exchanger andinvolves the burning of fuel and the passing of heated air through fluepipes in a curing barn. Accordingly, in this older version of the curingprocess, primarily radiant heat emanating from the flue pipes is used tocure the tobacco leaves. While a relatively low flow of air does passthrough the curing barn, this process utilizes primarily radiant heatemanating from the flue pipes to cure the tobacco leaves within thebarn. In addition, this process does not appreciate, and does notprovide for, controlling the conditions within the barn to achieveprevention or reduction of TSNAs. This technique has been largelyreplaced in the United States by a different flue-curing process.

For more than twenty years, the heat exchanger method described abovehas been supplanted in the U.S. with a more economical version whichfeatures the use of a propane burner. This second method is theso-called “flue curing” method. This process involves placing thetobacco leaves in a barn and subjecting the leaves to curing with theapplication of convective heat using a hot gaseous stream that includescombustion exhaust gases. When convective heat is used to dry thetobacco leaves, the combustion exhaust gases (including carbon monoxide,carbon dioxide, and water) are passed directly through the tobacco. Inprocesses where convective heat is used for curing, no attempt is madeto separate the heat from the combustion exhaust gases (i.e., to preventan anaerobic condition) or to control the ambient conditions to reduceor suppress the formation of TSNAs.

The third method is known as “air curing.” This process involves placingthe tobacco leaves in a barn and subjecting the leaves to air curingwithout controlling the ambient conditions (e.g., air flow through thebarn, temperature, humidity, and the like) and without the applicationof any heat.

U.S. Pat. No. 2,758,603 to Heljo discloses a process for treatingtobacco with relatively low moisture levels (i.e., already curedtobacco) with radio frequency energy to accelerate the aging process.Although the patent states that the tobacco being treated is “green”tobacco, it is clear that the patent is using the term “green” in anon-conventional sense because the tobacco being treated therein isalready cured (i.e., the tobacco is already dried). This is clearlyevident from the disclosed moisture levels for the tobacco being treatedin the Heljo patent. In fact, Heljo rehydrates the fully cured tobaccoprior to the radio frequency treatment. By contrast, in the presentinvention, the term “green tobacco” refers to freshly harvested tobacco,which contains relatively high levels of moisture.

Additionally, the use of microwave energy to dry agricultural productshas been proposed. For example, use of microwave energy to cure tobaccois disclosed in U.S. Pat. No. 430,806 to Hopkins. Further, U.S. Pat. No.4,898,189 to Wochnowski teaches the use of microwaves to treat greentobacco in order to control moisture content in preparation for storageor shipping. In U.S. Pat. No. 3,699,976, microwave energy is describedto kill insect infestation of tobacco. Still further, techniques usingimpregnation of tobacco with inert organic liquids (U.S. Pat. No.4,821,747) for the purposes of extracting expanded organic materials bya sluicing means have been disclosed wherein the mixture was exposed tomicrowave energy. In another embodiment, microwave energy is disclosedas the drying mechanism of extruded tobacco-containing material (U.S.Pat. No. 4,874,000). In U.S. Pat. No. 3,773,055, Sturgis discloses theuse of microwave to dry and expand cigarettes made with wet tobacco.

Using a novel breakthrough curing technology, U.S. Pat. No. 5,803,081 toWilliams discloses a method of reducing the nitrosamine levels orpreventing the formation of nitrosamines in a harvested tobacco plantusing microwave energy.

In U.S. Pat. No. 6,338,348 to Williams, a process for reducing theamount of or preventing the formation of nitrosamines in harvestedtobacco plant is disclosed, wherein the process comprises subjecting atleast a portion of the plant to microwave radiation, while the portionis uncured and in a state susceptible to having the amount ofnitrosamines reduced or formation of nitrosamines arrested, for a timesufficient to reduce the amount of, or substantially prevent formationof, at least one nitrosamine.

Further, U.S. Pat. No. 6,311,695 to Williams discloses that microwaveand other types of radiation are useful for treating tobacco to reducethe amount of, or prevent the formation of, nitrosamines in tobacco.

BRIEF SUMMARY OF THE INVENTION

It has now been discovered that by controlling the conditions to whichtobacco leaves are subjected to within the curing barn during the curingprocess, the formation of TSNAs in the tobacco product can be preventedor reduced. The parameters that can be varied to control the conditionswithin the curing barn (or curing apparatus) during the curing processinclude humidity, rate of temperature change, temperature, the time oftreatment of the tobacco, the airflow (through the curing apparatus orbarn), CO level, CO₂ level, O₂ level, and the arrangement of the tobaccoleaves.

By controlling the conditions during the curing process within certainparameters, it is believed that it is now possible to prevent or reducethe formation of microbes capable of causing the formation of TSNAs inthe tobacco. Thus, under the conditions contemplated for the presentinvention, it is believed that there would be little or no nitritesavailable for the formation of TSNAs by reaction of the nitrites withvarious tobacco alkaloids. For example, it is postulated that if theconditions are made aerobic, the microbes will consume the oxygen in theatmosphere for their energy source, and therefore no nitrites will form.Further, it is believed that the microbes are “obligate” anaerobes, andthus when they are subjected to certain conditions, they will besuppressed and cannot participate in the formation of nitrites.

Accordingly, one object of the present invention is to substantiallyeliminate or reduce the content of nitrosamines in tobacco intended forsmoking or consumption by other means.

Another object of the present invention is to reduce the carcinogenicpotential of tobacco products, including cigarettes, cigars, chewingtobacco, snuff and tobacco-containing gum and lozenges.

Still another object of the present invention is to substantiallyeliminate or significantly reduce the amount of tobacco-specificnitrosamines, including N′-nitrosonornicotine (NNN),4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK),N′-nitrosoanatabine (NAT) and N′-nitrosoanabasine (NAB), in such tobaccoproducts.

Another object of the present invention is to treat uncured tobacco atan appropriate time post-harvest so as to arrest the curing processwithout adversely affecting the tobacco's suitability for humanconsumption.

Another object of the present invention is to reduce the content oftobacco-specific nitrosamines by treating uncured tobacco in acontrolled environment.

Yet another object of the present invention is to reduce the content oftobacco-specific nitrosamines, particularly NNN and NNK, and metabolitesthereof in humans who smoke, consume or otherwise ingest tobacco in someform, by providing a tobacco product suitable for human consumption,which product contains a substantially reduced quantity oftobacco-specific nitrosamines, thereby lowering the carcinogenicpotential of such product. The tobacco product may be a cigarette,cigar, chewing tobacco or a tobacco-containing gum or lozenge.

Yet another object is to provide a novel curing barn (or curingapparatus) which is capable of providing tobacco suitable for humanconsumption, wherein the tobacco contains relatively low levels to zerotobacco-specific nitrosamines.

In one embodiment, the above and other objects and advantages inaccordance with the present invention can be obtained by a process forreducing the amount of or preventing the formation of nitrosamines in aharvested tobacco plant, comprising subjecting at least a portion of theplant, while said portion is uncured and in a state susceptible tohaving the amount of nitrosamines reduced or formation of nitrosaminesarrested, to a controlled environment capable of providing a reductionin the amount of nitrosamines or prevention of the formation ofnitrosamines, for a time sufficient to reduce the amount of orsubstantially prevent the formation of at least one nitrosamine, whereinsaid controlled environment is provided by controlling at least one ofhumidity, rate of temperature change, temperature, airflow, CO level,CO₂ level, O₂ level, and the arrangement of the tobacco leaves.

In a preferred embodiment of the invention, the step of subjectingtobacco leaf to the controlled environment is carried out on a tobaccoleaf or portion thereof after onset of yellowing in the leaf and priorto substantial accumulation of tobacco-specific nitrosamines in theleaf. It is also preferred that in the process of the invention, thestep of subjecting the tobacco leaf to the controlled environment iscarried out prior to substantial loss of the leafs cellular integrity.

It is also preferred in accordance with the present invention that thetobacco leaf or a portion thereof is subjected to the controlledenvironment for a time sufficient to effectively dry the leaf, withoutany charring when heat is applied, so that it is suitable for humanconsumption.

The present invention also seeks to subject tobacco leaves to thecontrolled environment to prevent normal accumulation of at least onetobacco-specific nitrosamine, such as N′-nitrosonornicotine,4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N′-nitrosoanatabineand N′-nitrosoanabasine.

In another embodiment, the process of the invention further comprisestreating the tobacco leaves, while in a state susceptible to having thecontent of at least one TSNA prevented or reduced, to microwave energyor other forms of high energy treatment.

The present invention in its broadest forms also encompasses a tobaccoproduct comprising non-green tobacco suitable for human consumption andhaving a lower content of at least one tobacco-specific nitrosamine thanconventionally cured tobacco.

In another embodiment, the present invention relates to a novel curingbarn which is capable of providing a controlled environment in which theformation of tobacco-specific nitrosamines can be prevented or reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a tobacco-curing apparatus according to the presentinvention.

FIG. 2 illustrates the air-handling device/heat exchanger system of thetobacco-curing apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the invention, the phrase “controlling the conditions”means determining and selecting an appropriate humidity, rate oftemperature change, temperature, time of treatment of the tobacco,airflow, CO level, CO₂ level, O₂ level, and arrangement of the tobaccoleaves to prevent or reduce the formation of at least one TSNA. For agiven set of ambient conditions, it may be necessary to adjust, withinthe curing apparatus or barn, one or more of these parameters. Forexample, it is possible to prevent or reduce the formation of TSNAs bysimply setting a high airflow through the curing apparatus or barn. Inother situations, it is possible to produce the tobacco products of thepresent invention with low airflow, provided that other parameters suchas humidity, temperature, etc. are appropriately selected.

In this disclosure, tobacco that has been “conventionally cured” istobacco that has been air-cured or flue-cured, without the controlledconditions described herein, according to conventional methods commonlyand commercially used in the U.S.

Further, the term “green tobacco” means tobacco that is substantiallyuncured and is particularly inclusive of freshly harvested tobacco.

In flue curing processes that utilize a heat exchanger capable ofproviding relatively low airflow through the curing barn, I havediscovered that it is possible to somewhat reduce the TSNA levels by notventing combustive exhaust gases into the curing apparatus or barn. Thepreferred aspects of the present invention are premised on the discoverythat other parameters, as identified above (e.g., airflow), can beadjusted to ensure the prevention or reduction of at least one TSNAregardless of the ambient conditions. Thus, even under the most extremeconditions (i.e., conditions that enhance the formation of TSNAs), it ispossible to achieve the prevention or reduction of at least one TSNA.

It has been said that the practice of tobacco curing is more of an artthan a science, because curing conditions during any given cure must beadjusted to take into account such factors as varietal differences,differences in leaves harvested from various stalk positions,differences among curing barns in terms of where they are used, andenvironmental variations during a single season or over multipleseasons, especially in terms of weather fluctuations during air-curing.For example, the practice of flue curing is empirical to a certaindegree, and is optimally carried out by individuals who have accumulatedexperience in this art over a significant period of time. See, e.g.,Peele et al, “Chemical and Biochemical Changes During The Flue Curing OfTobacco,” Recent Advances In Tobacco Science, Vol. 21, pp. 81 et seq.,Symposium Proceedings 49th Meeting Chemists' Research Conference, Sep.24-27, 1995, Lexington, Ky. (hereinafter “Peele et al”). Thus, one ofordinary skill in the art of tobacco curing would understand that theouter parameters of the present invention, in its broadest forms, arevariable to a certain extent depending on the precise confluence of theabove factors for any given harvest.

In one embodiment, the present invention is founded on the discoverythat a window exists during the tobacco curing cycle, in which thetobacco can be treated in a manner that will essentially prevent theformation of TSNA. Of course, the precise window during which TSNAformation can be effectively eliminated or substantially reduced dependson the type of tobacco and a number of other variables, including thosementioned above. In accordance with this embodiment of the presentinvention, the window corresponds to the time frame post-harvest whenthe leaf is beyond the fresh-cut or “green” stage, and prior to the timeat which TSNAs and/or nitrites substantially accumulate in the leaf.This time frame typically corresponds to the period in which the leaf isundergoing the yellowing process or is in the yellow phase, before theleaf turns brown, and prior to the substantial loss of cellularintegrity. (Unless otherwise clear from the context, the terms“substantial” and “significant” as used herein generally refer topredominant or majority on a relative scale, give or take.) During thistime frame, the leaves are susceptible to having the formation of TSNAssubstantially prevented, or the content of any already formed TSNAreduced, by subjecting the tobacco to a controlled environment capableof providing a reduction in the amount of nitrosamines or prevention ofthe formation of nitrosamines, for a time sufficient to reduce theamount of or substantially prevent the formation of at least onenitrosamine, wherein said controlled environment is provided bycontrolling at least one of humidity, rate of temperature change,temperature, airflow, CO level, CO₂ level, O₂ level, and arrangement ofthe tobacco leaves. This treatment of the tobacco essentially arreststhe natural formation of TSNAs, and provides a dried, golden yellow leafsuitable for human consumption. If TSNAs have already begun tosubstantially accumulate, typically toward the end of the yellowingphase, the treatment according to the present invention effectivelyarrests the natural TSNA formation cycle, thus preventing any furthersubstantial formation of TSNA. When yellow or yellowing tobacco istreated in this fashion at the most optimal time in the curing cycle,the resulting tobacco product has TSNA levels essentially approximatingthose of freshly harvested green tobacco, while maintaining its flavorand taste. In addition, the nicotine content of the tobacco productaccording to the present invention remains unchanged, or issubstantially unchanged, by the treatment according to the presentinvention. Accordingly, the tobacco product of the present invention hasrelatively low contents of TSNAs, and yet the user of the tobaccoproduct can experience the same sensations that are obtainable fromusing conventional tobacco products.

As discussed above, it is believed that tobacco-specific TSNAs areformed primarily during the curing process. Specifically, it is believedthat the amount of TSNAs in cured tobacco leaf is dependent on theaccumulation of nitrites, which are formed during the curing process byreduction of nitrates to nitrites under conditions approaching ananaerobic (i.e., oxygen deficient) environment. The nitrites accumulateduring the death of the plant cell. Experimental evidence suggests thatthe nitrites are formed by the micro flora on the surface of the leafunder conditions approaching an anaerobic environment. If, for example,conditions are made aerobic, the microbes will consume the oxygen in theatmosphere for their energy source, and thus, no nitrites will form.Once nitrites are formed, however, they can then combine with varioustobacco alkaloids, including pyridine-containing compounds, to formcarcinogenic substances such as nitrosamines.

In one conventional curing technique, the combustion exhaust gases passthrough the tobacco, thereby creating a condition approaching ananaerobic environment. This conventional curing technique utilizes airthat is normally recirculated within the curing barn and is often airhaving high humidity. Conventional curing has been developed over timewithout any appreciation for subjecting tobacco to a controlledenvironment for the purpose of eliminating or reducing TSNAs.Accordingly, such conventional curing techniques do not provide suitableconditions (e.g., adequate oxygen flow) and fail to prevent an anaerobiccondition in the vicinity of the tobacco leaves. Additionally, duringsuch conventional curing processes, the tobacco leaves will emit carbondioxide, which will further dilute the oxygen present in the curingenvironment. Under such anaerobic conditions, it is believed that themicro flora reduce nitrates to nitrites. Consequently, TSNA are formedand become part of the tobacco product that is ultimately consumed bythe tobacco user.

The present invention is applicable to the treatment of harvestedtobacco, which is intended for human consumption. Much research has beenperformed on tobacco, with particular reference to tobacco-specificnitrosamines (i.e., TSNAs). Freshly harvested tobacco leaves are called“green tobacco” and contain no known carcinogens, but green tobacco isnot suitable for human consumption. The process of curing green tobaccodepends on the type of tobacco harvested. For example, Virginia flue(bright) tobacco is typically flue-cured, whereas Burley and certaindark strains are usually air-cured. The flue-curing of tobacco typicallytakes place over a period of five to seven days compared to about one totwo or more months for air-curing. According to Peele et al, flue-curinghas generally been divided into three stages: yellowing (35-40° C.) forabout 36-72 hours (although others report that yellowing begins soonerthan 36 hours, e.g., at about 24 hours for certain Virginia fluestrains), leaf drying (40-57° C.) for 48 hours, and midrib (stem) drying(57-75° C.) for 48 hours. Many major chemical and biochemical changesbegin during the yellowing stage and continue through the early phasesof leaf drying.

In a typical flue-curing process, the yellowing stage is carried out ina barn. During this phase the green leaves gradually lose color due tochlorophyll degradation, with the corresponding appearance of the yellowcarotenoid pigments. According to the review by Peele et al, theyellowing stage of flue-curing tobacco is accomplished by closingexternal air vents in the barn, and holding the temperature atapproximately 35°-37° C. The yellowing stage typically lasts about 3 to5 days. After the yellowing stage, the air vents are opened, and theheat is gradually and incrementally raised. Over a period of about 5 to7 days from the end of yellowing, the tobacco product is dried. Thus,this process utilizes a somewhat controlled environment, but thecontrolled environment is insufficient to ensure the prevention orreduction of nitrosamines as in the present invention. Specifically, theprocess during the yellowing maintains the relative humidity in the barnat approximately 85%, limits moisture loss from the leaves, and allowsthe leaf to continue the metabolic processes that has begun in thefield. The goal of the flue-curing process is merely to obtain a dryproduct that has a lemon or golden orange color. In the flue-curingprocess, there is no appreciation for subjecting the tobacco leaves to aset of controlled conditions in order to ensure the prevention orreduction of TSNAs.

With one particular variety of Virginia flue tobacco on which testinghas been carried out as described herein, freshly harvested greentobacco is placed in a barn for about 24-48 hours at about 100-110° F.until the leaves turn more or less completely yellow. The yellow tobaccohas a reduced moisture content, i.e., from about 90 weight % when green,versus about 70-40 weight % when yellow. At this stage, the yellowtobacco contains essentially no known carcinogens, and the TSNA contentis essentially the same as in the fresh-cut green tobacco. This Virginiaflue tobacco typically remains in the yellow stage for about 6-7 days.At the end of curing, Virginia flue tobacco typically has a moisturecontent of about 11 to about 15 weight percent. The conversion of thetobacco during the curing process results in formation and substantialaccumulation of nitrosamines, and an increased microbial content. Theexact mechanism by which tobacco-specific nitrosamines are formed is notclear, but is believed to be enhanced by microbial activity, involvingmicrobial nitrate reductases in the generation of nitrite during thecuring process.

As previously mentioned, tobacco-specific nitrosamines are believed tobe formed upon reaction of amines with nitrite-derived nitrosatingspecies, such as NO₂, N₂O₃ and N₂O₄ under acidic or anaerobicconditions. Wiernik et al discuss the postulated formation of TSNAs atpp. 43-45, the discussion being incorporated herein by reference; abrief synopsis is set forth below.

Tobacco leaves contain an abundance of amines in the form of aminoacids, proteins, and alkaloids. The tertiary amine nicotine (referencedas (1) in the diagram below) is the major alkaloid in tobacco, whileother nicotine-type alkaloids are the secondary amines nornicotine (2),anatabine (3) and anabasine (4). Tobacco also generally contains up to5% of nitrate and traces of nitrite.

Nitrosation of nornicotine (2), anatabine (3), and anabasine (4) givesthe corresponding nitrosamines: N′-nitrosonornicotine (NNN, 5),N′-nitrosoanatabine (NAT, 6), and N′-nitrosoanabasine (NAB, 7).Nitrosation of nicotine (1) in aqueous solution affords a mixture of4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK, 8) (NNN, 5) and4-(N-nitrosomethylamino)-4-(3-pyridyl)-1-butanal (NNA, 9). Less commonlyencountered TSNAs include NNAL(4-N-nitrosomethylamino)-1-(3-pyridyl)-1-butanol, 10), iso-NNAL(4-N-nitrosomethylamino)-4-(3-pyridyl)-1-butanol, 11) and iso-NNAC(4-(N-nitrosomethylamino)-4-(3-pyridyl)-butanoic acid, 12). Theformation of these TSNAs from the corresponding tobacco alkaloids isshown schematically below, using the designations 1-12 above (reproducedfrom Wiernik et al, supra, p. 44, and incorporated herein by reference):

It is now generally agreed that green, freshly harvested tobaccocontains virtually no nitrite or TSNA, and that these compounds aregenerated during curing and storage of tobacco. Studies have been madeduring the past decade to try to determine the events related to theformation of TSNA during curing of tobacco, and several factors ofimportance have been identified. These include plant genotype, plantmaturity at harvest, curing conditions and microbial activity.

Studies have shown that nitrite and TSNA accumulate on air-curing at thetime intervals starting after the end of yellowing and ending when theleaf turns completely brown, e.g., 2-3 weeks after harvest for certainair-cured strains, and approximately a week or so after harvest influe-cured varieties. This is the time during which loss of cellularintegrity occurs, due to moisture loss and leakage of the content ofcells into the intercellular spaces. Therefore, there is a short windowin time during air-curing when the cells have disintegrated, making thenutrition available for microorganisms. Wiernik et al have suggestedthat nitrite may then substantially accumulate as a result ofdissimilatory nitrate reduction, thus rendering formation of TSNApossible.

There are a few published reports on the effects of microbial flora onthe tobacco leaf during growth and curing and on cured tobacco, as citedin Wiernik et al. However, the involvement of microbial nitritereductases in the generation of nitrate during curing is presumed. Whencell structure is broken down after the yellow phase, and nutrients aremade accessible to invading microorganisms, these may produce nitriteunder favorable conditions, i.e., high humidity, optimal temperature andanoxia. There is normally a rather short “window” in time when the wateractivity is still sufficiently high, and the cell structure hasdisintegrated.

In accordance with one embodiment of the present invention, theformation of nitrosamines in a harvested tobacco plant is substantiallyprevented or arrested by a process, comprising subjecting at least aportion of the plant, while said portion is uncured and in a statesusceptible to having the amount of nitrosamines reduced or formation ofnitrosamines arrested, to a controlled environment capable of providinga reduction in the amount of nitrosamines or prevention of the formationof nitrosamines, for a time sufficient to reduce the amount of orsubstantially prevent the formation of at least one nitrosamine, whereinsaid controlled environment is provided by controlling at least one ofhumidity, rate of temperature change, temperature, airflow, CO level,CO₂ level, O₂ level, and arrangement of the tobacco leaves.

In accordance with preferred embodiments of the present invention,non-green and/or yellow tobacco products can be obtained which aresuitable for human consumption, and which have a lower content of atleast one tobacco-specific nitrosamine than conventionally curedtobacco. Green or fresh-cut tobacco is generally unsuitable for humanconsumption as noted above; “non-green” as used herein means the tobaccohas at least lost the majority of chlorophyll, and includes withoutlimitation partially yellow leaves, full yellow leaves, and leaves whichhave begun to turn brown in places.

The present invention is applicable to all strains of tobacco, includingflue or bright varieties, Burley varieties, dark varieties,oriental/Turkish varieties, etc. Within the guidelines set forth herein,one of ordinary skill in the art could determine the most efficient timein the cure cycle for carrying out the treatment step to achieve theobjects and advantages of the present invention.

Although the airflow through the barn may vary on a case-by-case basisand may be dependent on the arrangement of the tobacco leaves to betreated (i.e., the degree of tobacco leaf surface exposure) and the sizeof the curing apparatus or barn, the minimum flow of air is preferablyabout ten percent higher than the flow of flue gas commonly used in theprior art. As discussed above, however, it is within the scope of thepresent invention to provide relatively low airflow, provided that otherparameters (e.g., humidity, temperature, etc.) are selected so that theprevention or reduction of at least one TSNA is achieved.

The specific minimum flow of air needed for a given set of conditionsmay be determined on a routine basis given the disclosure of the presentinvention.

To maximize the effects of the present invention, the humidity of theheated or unheated air is desirably controlled using acommercially-available dehumidifier or humidifier. Preferably, theheated or unheated air flow comprises dehumidified air with a humiditylevel of less than about 85%, more preferably less than about 60%, mostpreferably less than about 50%.

In one aspect, the air is fresh outside air, while the heated air issubstantially free from combustion exhaust gases including water vapor,carbon monoxide, and carbon dioxide.

In addition, the air may be recirculated as long as an anaerobiccondition is avoided.

The temperature within the curing barn of the present invention mayrange from ambient (i.e., outside) temperature to as high as about 250°F. or more, without charring the tobacco product. If heated air (i.e.,convective heat) is used to accelerate the drying of the tobaccoproduct, suitable temperatures may range anywhere from about 100° F. toabout 250° F., more preferably from about 160° F. to about 170° F.However, the optimum temperature within the curing barn can bedetermined for each case, depending on the overall conditions of theenvironment and the tobacco product being treated.

The determination of the time for treating the tobacco according to theprocess of the present invention can be determined by trial and error.Typically, the treatment time may be from about 48 hours up to about 2weeks.

The arrangement of the tobacco leaves is not critical, but it isadvantageous to provide the highest exposed surface area for the tobaccoleaves.

While it is not essential, it may be desirable to expose the tobaccoproduct to UV light, either simultaneously with, or separately from, thetreatment described above. It is believed that this UV light exposurecan further reduce the amount of TSNA accumulation. For example, the UVlight can be supplied using “Germicidal Sterilamp” tubes obtained fromPhilips Lighting, wherein the light has wavelengths of between 100 and280 nm.

Although the curing process as described above is preferable overmicrowave curing techniques because microwaving requires moist tobaccowhereas the inventive curing process does not, it is within the scope ofthe present invention to further treat the tobacco product withmicrowave or other high energy treatment, as described in U.S. Pat. Nos.6,338,348 and 6,311,695, respectively, both of which are incorporatedherein by reference. This additional microwave or other high energytreatment is conveniently performed within the window of time in whichit is possible to further prevent or reduce the formation of at leastone TSNA. While U.S. Pat. Nos. 6,338,348 and 6,311,695 are incorporatedherein by reference, the preferred aspects of the microwaving or otherhigh energy treatment are described below.

The process of this invention may further comprise a microwaving processfor reducing the amount of or preventing formation of nitrosamines in aharvested tobacco plant, which microwaving process comprises subjectingat least a portion of the plant to microwave radiation, while saidportion is uncured and in a state susceptible to having the amount ofnitrosamines reduced or formation of nitrosamines arrested, for asufficient time to reduce the amount of or substantially preventformation of at least one nitrosamine.

It is preferred that in this aspect of the process of the invention, thestep of subjecting to microwave radiation is carried out on a tobaccoleaf or portion thereof after onset of yellowing in the leaf and priorto substantial accumulation of tobacco-specific nitrosamines in theleaf. It is also preferred that in this aspect of the process of theinvention, the step of subjecting to microwave radiation is carried outprior to substantial loss of the leafs cellular integrity. Usingmicrowave energy eliminates the potential for activation of the microbesthat cause TSNAs in tobacco, particularly in tobacco that has beenrehydrated.

The term “microwave radiation” as used herein refers to electromagneticenergy in the form of microwaves having a frequency and wavelengthtypically characterized as falling within the microwave domain. The term“microwave” generally refers to that portion of the electromagneticspectrum which lies between the far-infrared region and the conventionalradio frequency spectrum. The range of microwaves extends from awavelength of approximately 1 millimeter and frequency of about 300,000MHz to wavelength of 30 centimeters and frequency of slightly less thanabout 1,000 MHz. The present invention preferably utilizes high powerapplications of microwaves, typically at the lower end of this frequencyrange. Within this preferred frequency range, there is a fundamentaldifference between a heating process by microwaves and by a classicalway, such as by infrared (for example, in cooking): due to a greaterpenetration, microwaves generally heat quickly to a depth severalcentimeters while heating by infrared is much more superficial. In theUnited States, commercial microwave apparatuses, such as kitchenmicrowave ovens, are available at standard frequencies of approximately915 MHz and 2450 MHz, respectively. These frequencies are standardindustrial bands. In Europe, microwave frequencies of 2450 and 896 MHzare commonly employed. Under properly balanced conditions, however,microwaves of other frequencies and wavelengths would be useful toachieve the objects and advantages of the present invention.

Microwave energy can be generated at a variety of power levels,depending on the desired application. Microwaves are typically producedby magnetrons, at power levels of 600-1000 watts for conventionalkitchen-level microwave apparatuses (commonly at about 800 watts), butcommercial units are capable of generating power up to several hundredkilowatts, generally by addition of modular sources of about 1 kilowatt.A magnetron can generate either pulsed or continuous waves of suitablyhigh frequency.

The applicator (or oven) is a necessary link between the microwave powergenerator and the material to be heated. For purposes of the presentinvention, any desired applicator can be used, so long as it is adaptedto permit the tobacco plant parts to be effectively subjected to theradiation. The applicator should be matched to the microwave generatorto optimize power transmission, and should avoid leakage of energytowards the outside. Multimode cavities (microwave ovens), thedimensions of which can be larger than several wavelengths if necessaryfor large samples, are useful. To ensure uniform heating in the leaves,the applicator can be equipped with a mode stirrer (a metallic movingdevice which modifies the field distribution continuously), and with amoving table surface, such as a conveyor belt. The best results areattained by single leaf thickness exposure to microwave radiation, asopposed to stacks or piles of leaves.

In preferred embodiments of the invention, the microwave conditionscomprise microwave frequencies of about 900 MHz to about 2500 MHz, morepreferably about 915 MHz and about 2450 MHz, power levels of from about600 watts up to 300 kilowatts, more preferably from about 600 to about1000 watts for kitchen-type applicators and from about 2 to about 75kilowatts, more preferably from about 5 to about 50 kilowatts, forcommercial multimode applicators. The heating time generally ranges fromat least about 1 second, and more generally from about 10 seconds up toabout 5 minutes. At power levels of about 800-1000 watts the heatingtime is preferably from about 1 minute to about 2½ minutes when treatingsingle leaves as opposed to piles or stacks. For commercial-scaleapplicators using higher power levels in the range of, e.g., 2-75kilowatts, heating times would be lower, ranging from about 5 seconds upto about 60 seconds, and generally in the 10-30 second range at, say, 50kilowatts, again for single leaves as opposed to piles or stacks. Ofcourse, one of ordinary skill in the art would understand that anoptimal microwave field density could be determined for any givenapplicator based on the volume of the cavity, the power level employed,and the amount of moisture in the leaves. Generally speaking, use ofhigher power levels will require less time during which the leaf issubjected to the microwave radiation.

However, the above-described conditions are not absolute, and given theteachings of the present invention, one of ordinary skill in the artwould be able to determine appropriate microwave parameters. Themicrowave radiation is preferably applied to the leaf or portion thereoffor a time sufficient to effectively dry the leaf, without charring, sothat it is suitable for human consumption. It is also preferred to applythe microwave radiation to the leaf or portion thereof for a time and ata power level sufficient to reduce the moisture content to below about20% by weight, more preferably about 10% by weight.

It is also preferred in accordance with the present invention that themicrowave radiation is applied to the leaf or portion thereof for a timesufficient to effectively dry the leaf, without charring, so that it issuitable for human consumption.

It is also possible to use forms of electromagnetic radiation havinghigher frequencies and shorter wavelengths than the microwave domaindiscussed above and in more detail below, can be used to achieve thebasic objects of the present invention—reduction or substantialelimination of TSNAs in tobacco products, by treating the tobacco withsuch energy forms in the same time frame post-harvest as discussed abovewith regard to the microwave embodiment. Thus, the present inventionfurther comprises a method for reducing the amount of or preventingformation of nitrosamines in a harvested tobacco plant, comprisingsubjecting at least a portion of the plant to radiation having afrequency higher than the microwave domain, while said portion isuncured and in a state susceptible to having the amount of nitrosaminesreduced or formation of nitrosamines arrested, for a sufficient time toreduce the amount of or substantially prevent formation of at least onenitrosamine.

As with the microwave embodiments, it is preferred that in the processof the invention, the step of subjecting to radiation having a frequencyhigher than the microwave domain is carried out on a tobacco leaf orportion thereof after onset of yellowing in the leaf and prior tosubstantial accumulation of tobacco-specific nitrosamines in the leaf.It is also preferred that in the process of the invention, the step ofsubjecting to such radiation is carried out prior to substantial loss ofthe leafs cellular integrity. Preferred energy sources capable ofproducing such radiation are described further below, and includefar-infrared and infrared radiation, UV (ultraviolet radiation), softx-rays or lasers, accelerated particle beams such as electron beams,x-rays and gamma radiation.

On a scale within the electromagnetic spectrum where microwaves aregenerally defined as inclusive of those forms of electromagneticradiation having a frequency of 10¹¹ Hz and a wavelength of 3×10⁻³meters, such energy sources include, without limitation, far-infraredand infrared radiation having frequencies of about 1012 to 1014 Hz andwavelengths of 3×10⁻⁴ to 3×10⁻⁶ meters, ultraviolet radiation havingfrequencies of about 10¹⁶ to 10¹⁸ Hz and wavelengths of 3×10⁻⁸ to3×10⁻¹⁰ meters, soft x-rays or lasers, cathode rays (a stream ofnegatively charged electrons issuing from the cathode of a vacuum tubeperpendicular to the surface), x-rays and gamma radiation typicallycharacterized as having frequencies of 10²¹ Hz and higher atcorresponding wavelengths.

As would be apparent to one of ordinary skill in the art, the greaterthe dose of radiation delivered by the energy source, the less time theleaves need to be subjected thereto to achieve the desired results.Typically, radiation application times of less than one minute,preferably less than 30 seconds and even more preferably less than aboutten seconds are needed when using such higher frequency radiationsources. Defined another way, radiation application times of at leastabout one second are preferred. However, the exposure rate can becontrolled to deliver the radiation dosage over time, if desired. Forexample, 1 megarad of radiation can be delivered instantaneously, or ata predetermined exposure rate. When using high frequency radiationsources, it is preferred to use an amount of radiation which achieves atleast a 50% reduction in TSNAs, in comparison to untreated samples.While the particular radiation dosages and exposure rate will depend onthe particular equipment and type of radiation source being applied, aswould be apparent to one of ordinary skill in the art, it is generallypreferred to subject the tobacco samples to radiation of from about 0.1to about 10 megarads, more preferably from about 0.5 to about 5megarads, and more preferably from about 0.75 to about 1.5 megarads.

It is preferred that the microwaving or other high energy treatment, asdescribed above, is conducted after subjecting the tobacco to thecontrolled environment of the present invention. However, it is alsopossible to conduct the optional microwaving or high energy treatmentprior to subjecting the tobacco to the controlled environment of thepresent invention.

The treatment according to the present invention, with or withoutmicrowaving or other high energy treatment, may be performed inconventional barns as well as large-scale processing centers capable oftreating tens of acres of tobacco. It is also possible to perform theprocess of the present invention in any size, including miniature curingapparatuses or barns.

On a bench scale, the treatment of the tobacco product according to thepresent invention, using airflow and temperature control, would besimilar to treating tobacco product using a convective heating air ovenor treating the tobacco product using a clothes dryer. Thus, it iswithin the present invention to operate the process of the presentinvention in a convective heating air oven or a clothes dryer, althoughthese apparatuses are not within the scope of the curing apparatus orbarns as defined in the appended claims.

In another embodiment, the present invention relates to a tobaccoproduct comprising cured non-green or yellow tobacco suitable for humanconsumption and having a content of at least one tobacco-specificnitrosamine selected from N′-nitrosonornicotine (NNN),4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK),N′-nitrosoanatabine (NAT) and N′-nitrosoanabasine (NAB) which is lessthan about 50% by weight of the content of said at least onetobacco-specific nitrosamine in conventionally cured tobacco, morepreferably less than about 75% by weight, most preferably less thanabout 95% by weight, without the use of organic solvent extraction.

Thus, it is possible to reduce the TSNA content by about 97% or more bypracticing the present invention, even down to “food safe” TSNA levels.

For example, the NNN level of the tobacco product according to thepresent invention is typically less than about 0.05 μg/g, the combinedNAT and NAB level is typically less than about 0.10 μg/g, and the NNKlevel is typically less than about 0.05 μg/g. Further, the combined TSNAlevel is typically less than about 0.16 μg/g, even as low as less thanabout 0.009 μg/g.

Thus, in yet another aspect of the present invention, the tobaccoproduct according to the present invention comprises cured non-green oryellow tobacco having a NNN content less than about 0.05 μg/g.

In a further aspect, the tobacco product of the present inventioncomprises cured non-green or yellow tobacco having a combined NAT andNAB content of less than about 0.10 μg/g.

Still further, the tobacco product of the present invention comprisescured non-green or yellow tobacco having a NNK content of less thanabout 0.05 μg/g.

Additionally, the present invention also contemplates tobacco productcomprising cured non-green or yellow tobacco having a total TSNA contentof less than about 0.16 μg/g.

In a preferred embodiment, the tobacco product of the present inventionhas a NNN level of less than about 0.05 μg/g, a combined NAT and NABlevel of less than about 0.10 μg/g, and a NNK level less than about 0.05μg/g.

The tobacco product according to the present invention can be convertedto various final tobacco products, including, but not limited to,cigarettes, cigars, chewing tobacco, snuff and tobacco-containing gumand lozenges.

In yet another embodiment, the present invention is directed to anapparatus for curing tobacco products comprising: an enclosed orsubstantially enclosed container comprising a base frame, optionally atleast one wall, optionally a roof, and optionally a door; an airhandling device capable of providing an air flow of at least about25,0000 CFM, wherein said air flow is at least partially and at leasttemporarily in communication with the interior of said container; and aheat exchanger capable of providing at least about 1,000,000 BTU/hr.

If desired, the container may be in the form of a mobile unit withtransport means. The container may be constructed to any suitable sizetypical of tobacco curing barns. For example, tile container may have awidth of about 120 inches, a depth of 60 inches, and a height of 82inches. It is possible to provide a container that is significantlysmaller or larger than this exemplified container size. In addition, thecontainer may be insulated.

The container may comprise means that are capable of receiving thetobacco products to be cured. Preferably, these means are arranged sothat the tobacco product is exposed for optimal curing.

Preferably, the air circulation within the container may be of avertical or horizontal draft design, with the flow of air being in anysuitable direction, with manually or automatically controlled fresh airdampers and weighted exhaust dampers.

The heat exchanger is preferably constructed of stainless steel. Theheat exchanger system is preferably supplied with a flame detector,igniter wire, sensor cable, dual valve gas train and/or air provingswitch. The burner setting can be variable. As mentioned previously,however, it is possible to carry out the process of the presentinvention without the use of any heat. That is, the process can beconducted using simply a sufficient flow of air.

In the present invention, the apparatus for curing the tobacco productsuses air that is free from combustion exhaust gases, such as carbonmonoxide and carbon dioxide. However, it should be noted that withsufficient airflow, the effects of the present invention can be realizedeven with air containing combustion exhaust gases.

Reference is now made to the drawings. FIG. 1 shows a container (1) andan air handling device/heat exchanger system (2). FIG. 2 shows the airhandling device/heat exchanger system (2) in greater detail. It can beseen from FIG. 2 that the exhausts (3) of the heat exchanger system isfar removed from the air intakes (4) to minimize the possibility ofcombustion exhaust gases being introduced into the curing apparatus.Further, unlike conventional curing barns, the curing apparatus of thepresent invention features an externalized air handling device/heatexchanger system.

The following examples illustrate the advantages of the presentinvention.

EXAMPLES

In each of the examples described below, five grams of ground tobaccowere placed in a 300-ml Erlenmeyer flask and suspended in 150-ml waterto which 5 ml of 20% ammonium sulfamate in 3.6 N H₂SO₄ was added toprevent the artificial formation of TSNA during extraction. Prior toshaking on the wrist-action shaker overnight, the flask was capped usingparafilm and wrapped up in aluminum foil to prevent degradation of TSNAby light. The TSNA were extracted.

The final TSNA extract (pH 9 fraction) was transferred quantitativeusing a Pasteur pipette into a 1 ml volumetric flask and adjusted forfull volume. Samples were stored in GC vials until GC-TEA analysis.

For the TSNA analysis, an aliquot of 0.1 ml was dried in a GC vial witha gentle stream of nitrogen and the GC standard (N-nitrosoguvacoline;3.2 ppm) in acetonitrile was added prior to analysis. The GC-TEA wascalibrated with a standard TSNA mixture on a daily basis, before andafter analyses of tobacco extracts.

GC Hewlett Packard Model 5890 and TEA™ Model 543 Analyzer were used.

Example 1

This experiment shows the advantages of the present invention on areduced scale.

Yellow tobacco leaf was finely diced with scissors and subjected tocuring for 45 minutes at 167° F. using convective heat in the form of ahot air stream substantially free from combustion exhaust gases. (A hotconvection air oven was used for this purpose.) The sample was rathermoist, and therefore, a wet weight was taken and calculations were madeto correct the TSNA content to dry weight basis. 75% of the leaf wasmoisture, and thus the wet weight was multiplied by 0.25 to obtain thedry weight. The results are tabulated in Table 1 below.

Although the treatment was made only for 45 minutes, longer or shortertreatment times are envisioned depending on the conditions and theresults desired.

Comparative Example 1

Instead of the convective heat treatment described in Example 1 above,yellow tobacco leaf was microwaved. The results are set forth in Table 1below.

Example 2

Instead of the convective heat treatment described in Example 1 above,yellow tobacco leaf (Virginia) was subjected to a modified flue-curingtechnique that eliminates the flow of combustion exhaust gases into thecuring barn. This was accomplished by using a heat exchanger. Thetreated tobacco was tested, and the results are given in Table 1. TABLE1 μg/g EXAMPLE μg/g NAT + μg/g μg/g NO. NNN NAB NNK TSNA Ex. 1 0.03100.0843 <0.0004 0.1157 Comp. Ex. 1 <0.0004 <0.0006 <0.0005 <0.00014 Ex. 20.0451 0.1253 0.0356 0.2061

As can be seen from Table 1, the process of the present inventionprovides tobacco having substantially reduced amounts of TSNA.

Example 3

Yellow tobacco leaf was treated with a flow of air using a MAYTAGclothes dryer under “fluff dry” at 85° F. in Example 3. The results areshown in Table 2.

Example 4

This experiment shows the efficacy of the present invention featuringdrying without the use of heat. In this example, yellow tobacco leaf wastreated with a flow of unheated air using a MAYTAG clothes dryer for sixhours. The results are shown in Table 2.

Comparative Example 2

Tobacco leaf was flue cured according to a predominant version of theconventional flue curing process in a curing barn. As is the commonpractice for such conventional flue-curing, the combustion exhaust gaseswere vented through the curing barn in this process. In thisconventional flue curing process, tobacco was placed in a barn withrelatively low flow of air and closed external air vents. Thetemperature was incrementally increased (about 0.5 to 1.5° F. per hour)to about 13° F. over a period of about 3 days. At this point (i.e., endof yellowing), the external air vents were opened, and the temperaturewas maintained at 130° F. for about 24-36 hours. The external air ventswere then closed and the temperature was raised to about 160° F. toinitiate the “killing out phase” (i.e., the phase in which the stem isdried) with relatively low air flow. It is important to note that in theconventional flue curing process, the air flow (any fresh air plus anyrecirculating air) is significantly lower than what is typically used inthe present invention. The results are shown in Table 2.

Comparative Example 3

Yellow tobacco leaf was microwaved for 60 seconds in a commercialtobacco microwaving plant. The results are shown in Table 2.

Comparative Example 4

Yellow tobacco leaf was again microwaved for 60 seconds in a commercialtobacco microwaving plant. The results are shown in Table 2. TABLE 2EXAMPLE μg/g μg/g μg/g μg/g NO. NNN NAT + NAB NNK TSNA Ex. 3 0.037 0.046<0.001 0.084 Ex. 4 0.042 0.054 <0.001 0.097 Comp. Ex. 2 0.77 0.89 1.373.03 Comp. Ex. 3 0.04 0.054 <0.001 0.095 Comp. Ex. 4 <0.001 0.042 <0.0010.044

Examples 3 and 4 provided very low levels of TSNA, especially NNN andNNK, even when microwaving was not used.

Example 5

Yellow tobacco leaf in the outer portion of a curing barn was subjectedto a flow of air for 7 days according to the present invention. Theresults are tabulated in Table 3.

Example 6

Yellow tobacco leaf in the inner portion of a curing barn was subjectedto a flow of air for 7 days according to the present invention. Theresults are tabulated in Table 3.

Comparative Example 5

Yellow tobacco leaf cured in a curing barn according to a conventionalcuring process was tested for TSNA levels. The results are shown inTable 3. TABLE 3 EXAMPLE μg/g μg/g μg/g μg/g NO. NNN NAT + NAB NNK TSNAEx. 5 0.03 ± .02 0.06 0.05 0.14 ± .02 Ex. 6 0.04 ± .01 0.08 ± .02 0.040.15 ± .01 Comp. Ex. 5 0.41 ± .04 1.16 ± .13 1.56 ± .21 3.14 ± .36

As is apparent from Table 3, the curing process according to the presentinvention provided unexpectedly lower levels of TSNA as compared to aconventional curing process.

Example 7

This example illustrates the advantageous effects obtainable bypracticing the present invention even under the most severeenvironmental conditions. Throughout all phases of the curing,combustion exhaust gases were not allowed to flow into the barn.

Green tobacco was left in a curing barn according to the presentinvention for about 72 hours with the external air vent closed, but withrecirculating air of about 25,000 CFM, and with heating of about 300,000BTUs to provide a temperature of about 1050 F. After this period ofabout 72 hours (end of yellowing), the external air vents were openedand the air handling device was adjusted to provide virtually all freshair flow of approximately 25,000 CFM (with only a minor amount ofrecirculating air), and the heat was increased to about 1,000,000 BTUsto provide a rapid temperature increase to about 140° F. This treatmentwas continued for about 72 hours. At this point, the “killing out” phase(i.e., drying of the stems) was initiated by closing the external airvents and increasing the temperature to about 160° F. Treatmentcontinued for about 1-2 days.

The resulting tobacco product was tested for TSNAs according to theanalytical technique described above. The levels for each individualnitrosamine were so low that they could not be detected.

1. A tobacco product comprising cured non-green or yellow Burley tobaccosuitable for human consumption, substantially free of organic liquidsused to extract expanded organic materials and having a collectivecontent of N′-nitrosonornicotine,4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N′-nitrosoanatabineand N′-nitrosoanabasine which is 0.05 μg/g or less.
 2. The tobaccoproduct of claim 1, wherein said tobacco suitable for human consumptionis cured yellow tobacco.
 3. The tobacco product of claim 1, which is aproduct selected from the group consisting of cigarettes, cigars,chewing tobacco, snuff and tobacco-containing gum and bits.
 4. A tobaccoproduct comprising cured non-green or yellow Burley tobacco suitable forhuman consumption, in leaf form and having a collective content ofN′-nitrosonornicotine,4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N′-nitrosoanatabineand N′-nitrosoanabasine which is 0.05 μg/g or less.
 5. The tobaccoproduct of claim 4, wherein said tobacco suitable for human consumptionis cured yellow tobacco.
 6. The tobacco product of claim 4, which is aproduct selected from the group consisting of cigarettes, cigars,chewing tobacco, snuff and tobacco-containing gum and bits.
 7. A tobaccoproduct comprising cured non-green or yellow Burley tobacco suitable forhuman consumption, substantially free of organic liquids used to extractexpanded organic materials and having a content of4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone which is 0.002 μg/g orless.
 8. The tobacco product of claim 7, wherein said content of4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone is 0.001 μg/g or less.9. The tobacco product of claim 7, wherein said tobacco suitable forhuman consumption is cured yellow tobacco.
 10. A tobacco productcomprising cured non-green or yellow Burley tobacco suitable for humanconsumption, in leaf form and having a content of4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone which is 0.002 μg/g orless.
 11. The tobacco product of claim 10, wherein said content of4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone is 0.001 μg/g or less.12. The tobacco product of claim 10, wherein said tobacco suitable forhuman consumption is cured yellow tobacco.
 13. A tobacco productcomprising cured non-green or yellow United States Burley tobaccosuitable for human consumption, substantially free of organic liquidsused to extract expanded organic materials and having a collectivecontent of N′-nitrosonornicotine,4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N′-nitrosoanatabineand N′-nitrosoanabasine which is less than 0.2 μg/g.
 14. The tobaccoproduct of claim 13, wherein said collective content is 0.15 μg/g orless.
 15. The tobacco product of claim 14, wherein said collectivecontent is 0.1 μg/g or less.
 16. The tobacco product of claim 15,wherein said collective content is 0.05 μg/g or less.
 17. The tobaccoproduct of claim 13, wherein said tobacco suitable for human consumptionis cured yellow tobacco.
 18. The tobacco product of claim 13, which is aproduct selected from the group consisting of cigarettes, cigars,chewing tobacco, snuff and tobacco-containing gum and bits.
 19. Atobacco product comprising cured non-green or yellow United StatesBurley tobacco suitable for human consumption, in leaf form and having acollective content of N′-nitrosonornicotine,4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N′-nitrosoanatabineand N′-nitrosoanabasine which is less than 0.2 μg/g.
 20. The tobaccoproduct of claim 19, wherein said collective content is 0.15 μg/g orless.
 21. The tobacco product of claim 20, wherein said collectivecontent is 0.1 μg/g or less.
 22. The tobacco product of claim 21,wherein said collective content is 0.05 μg/g or less.
 23. The tobaccoproduct of claim 19, wherein said tobacco suitable for human consumptionis cured yellow tobacco.
 24. The tobacco product of claim 19, which is aproduct selected from the group consisting of cigarettes, cigars,chewing tobacco, snuff and tobacco-containing gum and bits.